Devices and systems for liquid/liquid extraction have been used for many purposes in analytical and purification chemical arts. So for example it is possible to remove all or part of a particular component, i.e. a solute, from a solvent in which the solute has been dissolved, by treating the solution with a solvent having a greater affinity for the solute and which is only limitedly miscible with the first solvent. The system is agitated and allowed to settle whereupon the first solvent and the second solvent separate into layers, the solute having been prepared between them. The physical removal of one layer from the other may involve simple decanting from the other phase--i.e. the less dense phase--although this technique is not widely used because not all of the low-indensity phase can be recovered and a substantial danger of contamination exists.
It is more common, therefore, to provide a separation funnel which consists of a vessel surmounting a stopcock and discharge tube. The stopcock is opened to drain the lower face until the interface reaches the stopcock, the latter being then closed. While this system has significan advantages over simple decanting systems, it is characterized by a distribution coefficient between about 0.05 and 20.
It has been possible to increase the distribution coefficient markedly, e.g. to values between 10.sup.-3, using specially prepared phase-separation papers. This system has however, the disadvantage that an absorption of multivalent ions on the filter paper forming separation medium is unavoidable. When the process is used for trace analysis this is a serious disadvantage.
It has also been known heretofore to separate liquid phases used in solvent extraction by centrifugation. In this system, the liquid/liquid mixture is placed in centrifuge tubes and other vessels of various materials, e.g. glas, quartz, metal, synthetic resin, and accelerated to 2000 G or more whereupon the more dense phase tends to separate from the less dense phase because of the differences in response to centrifugal force which is a function of the mass of the material. Here too it is possible to reach distribution coefficients between 10.sup.-3 and 10.sup.3. These arrangements have, however, an important disadvantage in that it is not possible to recover a sample aliquot or all of a lower phase with a pipette or the like without traversing the upper phase and unavoidably contaminating the sample.
Other centrifuge systems including those operating with continuous phase separation with computer control centrifuges have also been employed but are not satisfactory for various reasons. Perticularly in radioactive activation work, the recovery of substances labeled with radioactive compounds and the separation by liquid/liquid extraction of radioactive substances cannot be effectively carried out in such continuous centrifuges because of the possibility of radioactive contamination and the consequent need for replacing contaminated parts. Furthermore, such continuous systems require more material than may abe available and are not satisfactory for recovery of short-lived radioactive species.